139
FXUS02 KWBC 030658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT SAT AUG 3 2024
VALID 12Z TUE AUG 06 2024 - 12Z SAT AUG 10 2024
...TROPICAL CYCLONE FOUR WILL THREATEN PARTS OF FLORIDA INTO THE
COASTAL SOUTHEAST INTO NEXT WEEK...
...HAZARDOUS HEAT PERSISTS ACROSS THE SOUTHWEST EARLY NEXT WEEK AS
HEAT INTENSIFIES OVER THE SOUTH-CENTRAL U.S. AS THE WEEK PROGRESSES...
..OVERVIEW
THE NATIONAL HURRICANE CENTER CONTINUES TO FORECAST TROPICAL
CYCLONE FOUR TO TRACK ACROSS FLORIDA INTO THE WESTERN ATLANTIC
OCEAN WITH A NOTABLE SLOW DOWN NEAR THE SOUTHEAST/CAROLINA COAST.
THIS TROPICAL SYSTEM WILL SPREAD HEAVY RAIN AND FLASH FLOODING, AS
WELL AS, GUSTY WINDS LINGERING IN FLORIDA AND PUSHING INTO THE
COASTAL SOUTHEAST FOR THE FIRST PART OF THE WEEK. THERE CONTINUES
TO BE UNCERTAINTY IN REGARDS TO THE TIMING AND HOW FAR INLAND THE
IMPACTS GET. FARTHER WEST, UPPER RIDGING CENTERED NEAR THE FOUR
CORNERS WILL MAINTAIN HEAT CONCERNS ACROSS THE WEST THROUGH PARTS
OF NEXT WEEK. THE RIDGING SHOULD GET SUPPRESSED BY SHORTWAVES IN
THE NORTHWEST BUT EXPAND EAST TO FOCUS POTENTIALLY HAZARDOUS HEAT
IN THE SOUTH-CENTRAL U.S. MID- TO LATE NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THERE CONTINUES TO BE A FAIR AMOUNT OF SPREAD AMONG THE GLOBAL AND
ENSEMBLE GUIDANCE IN REGARDS TO THE TRACK, TIMING AND STRENGTH OF
TROPICAL CYCLONE FOUR. THE LAST COUPLE OF RUNS DID REVEAL A SLOWING
TREND, ESPECIALLY FOR DAYS 3-5, AND FAVORED A TRACK THAT CROSSED
THE STATE OF FLORIDA (POSSIBLY SOUTHEAST GEORGIA) AND TRACK
NORTH/NORTHEAST OFFSHORE THE CAROLINA COAST EARLY NEXT WEEK. THE
GFS HAS BEEN PERSISTENTLY FASTER/DEEPER WITH THE TRACK WHILE THE
CMC AND UKMET HAVE BEEN SLOWER AND FURTHER INLAND. AS PREVIOUSLY
NOTED, THE ECWMF HAS BEEN A REASONABLE MIDDLE GROUND APPROACH THAT
REFLECTS A SLIGHTLY SLOWER TRACK BUT NOT WAS FAR WEST AS THE CMC
AND UKMET. THIS TYPE OF MIDDLE GROUND SOLUTION CONTINUED TO
COMPLIMENT THE NHC FORECAST.
THE WPC QPF WILL BE DEPENDENT ON HOW CLOSE TO LAND/INLAND THAT THE
STORM TRACKS AND THE SPEED OF THE SYSTEM. THE POSSIBLE EJECTION OF
THE STORM NORTHEASTWARD IS UNCERTAIN AS WELL, DEPENDING ON IF AN
UPPER TROUGH STEERS IT NORTHEAST. THERE HAS BEEN A TREND TO SUGGEST
THAT THE STORM RETROGRADES TOWARD THE APPALACHIANS/TENNESSEE
VALLEY FURTHER FORECAST ADJUSTMENTS WILL BE NEEDED AND SEE NHC FOR
THE OFFICIAL TRACK.
ELSEWHERE, UPPER RIDGING CENTERED NEAR THE FOUR CORNERS WEAKENING
A BIT WITH TIME IS AGREEABLE IN THE GUIDANCE, WHILE THE NORTHERN
STREAM SHORTWAVES ROUNDING THIS RIDGE AND MAKING THEIR WAY INTO THE
NORTHEASTERN U.S. SHOW MORE VARIABILITY. FRONTAL AND QPF
POSITIONING IN THE MIDWEST TO NORTHEAST VARIES BECAUSE OF THIS. A
BLEND OF MODELS/ENSEMBLES SEEMED REASONABLE THOUGH.
THE WPC FORECAST LEANED TOWARD THE 00Z ECMWF MORE SO THAN THE GFS
EARLY ON GIVEN ITS INITIALLY FAVORABLE TRACK WITH TROPICAL CYCLONE
FOUR. THE UKMET AND CMC WERE NOT UTILIZED FOR THIS FORECAST. THE
PROPORTION OF ENSEMBLE MEANS WERE INCREASED TO MORE THAN HALF BY
DAY 7 AS MODEL SPREAD INCREASED.
..WEATHER/HAZARDS HIGHLIGHTS
HEAVY RAIN IS EXPECTED TO ACCOMPANY THE TROPICAL CYCLONE ALONG ITS
PATH. GIVEN THE DEGREE OF UNCERTAINTY HOW MUCH OCCURS ONSHORE
VERSUS OFFSHORE WILL BE DEPENDENT ON THE EXACT TRACK THE STORMS
TAKES, ESPECIALLY WITH THE NOTABLE SLOWING TREND AS IT PROGRESSES
NORTHEAST. A SLIGHT RISK FOR EXCESSIVE RAINFALL WAS MAINTAINED FOR
THE DAY 4 PERIOD FOR EASTERN PORTIONS OF GEORGIA AND THE CAROLINAS.
IN ADDITION, A SLIGHT RISK WAS RAISED FOR THE DAY 5 TO ACCOUNT FOR
THE CONTINUED THREAT FOR HEAVY RAIN ALONG THE CAROLINA COAST AND
INTO SOUTHEAST VIRGINIA. THE MULTIDAY ACCUMULATION OF 8 TO 12
INCHES WITH LOCALLY HIGHER AMOUNTS IS THE CURRENT THOUGHT. THESE
RISK AREAS ATTEMPT TO FOLLOW THE CURRENT FORECAST TRACK OF TROPICAL
CYCLONE, I.E. OFFSHORE BUT NEAR ENOUGH TO LAND TO SPREAD HEAVY
RAIN AMOUNTS THAT MAY CAUSE FLASH FLOODING INLAND. EXPECT FURTHER
ADJUSTMENTS AS THE FORECAST EVOLVES.
MODELS CONTINUE TO SHOW A POTENTIAL MESOSCALE CONVECTIVE SYSTEM
RIDING THE TOP OF THE RIDGE INTO THE UPPER MIDWEST/UPPER GREAT
LAKES ON MONDAY. BY TUESDAY MOISTURE STREAMS COULD COMBINE IN THE
LOWER GREAT LAKES TO NORTHEAST TO FOCUS RAIN NEAR THE FRONT IN WHAT
MIGHT BE CONSIDERED A PREDECESSOR RAIN EVENT (PRE). LACK OF MODEL
CONSISTENCY IN PLACEMENT OF RAIN AMOUNTS PRECLUDED ANY EMBEDDED
SLIGHT RISK WITHIN THE LARGER MARGINAL AT THIS TIME.
MONSOONAL MOISTURE ON THE WESTERN SIDE OF THE RIDGE SHOULD KEEP A
WET AND UNSETTLED PATTERN IN PLACE FROM THE FOUR CORNERS REGION
NORTHWARD INTO THE ROCKIES/HIGH PLAINS THROUGH MUCH OF THE
EXTENDED PERIOD. MARGINAL RISKS FOR EXCESSIVE RAIN ARE IN EFFECT
FOR PARTS OF THE SOUTHWEST/FOUR CORNERS (ESPECIALLY THE SENSITIVE
SLOT CANYONS IN SOUTHERN UTAH) TUESDAY AND WEDNESDAY.
ABOVE SEASONAL NORMAL TEMPERATURES ACROSS THE WEST IS ANTICIPATED
TO GRADUALLY LOWER THROUGH THE EXTENDED PERIOD. THE SOUTHWEST
SHOULD SEE THE LONGEST-LASTING HEAT CONCERNS, WITH DAYTIME HIGHS
EXCEEDING 110F LIKELY, BUT THIS IS ONLY A FEW DEGREES ABOVE
AVERAGE. HAZARDOUS HEAT WILL BE LIKELY FOR THE CENTRAL/SOUTHERN
PLAINS AND MIDDLE/LOWER MISSISSIPPI VALLEY EARLY IN THE WEEK. MUCH
OF THE CENTRAL U.S. WILL COOL OFF IN THE WAKE OF A COLD FRONT
MIDWEEK; HOWEVER, EXCESSIVE HEAT WILL THEN FOCUS ACROSS THE
SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND SOUTHEAST.
EXPERIMENTAL HEATRISK VALUES ARE GENERALLY MAJOR FOR MUCH OF THIS
REGION TO EVEN EXTREME FOR THE CENTRAL GULF COAST AREA. THE NORTH-
CENTRAL U.S. SHOULD REMAIN NEAR TO BELOW NORMAL THROUGH THE PERIOD
AS WEAK SHORTWAVE ENERGIES MOVE THROUGH.
CAMPBELL/TATE
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC MEDIUM
RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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